1. Field of the Invention
The invention generally relates to fibrous consolidated composite articles, and to methods of making the same and, more specifically, the invention relates to composite articles made from the fibers of hemp hurd, kenaf, vegetable bamboo, and/or mixtures thereof.
2. Brief Description of Related Technology
One type of molded composite article is a cellulosic (or woody) composite which includes man-made boards of bonded wood sheets and/or lignocellulosic materials, commonly referred to in the art by the following exemplary terms: fiberboards such as hardboard, medium density fiberboard, and softboard; particleboards such as chipboard, flakeboard, particleboard, strandboard, and waferboard. Wood composites also include man-made boards comprising combinations of these materials. These wood composites can be used as columns, floors, ceilings, walls, doors, siding and stairs in the construction of homes, offices, and other types of buildings, as well as furniture components, such as chairs, tables, countertops, cabinets, and cabinet doors, for example.
Many different methods of manufacturing wood composites are known in the art such as, for example, those described in Hsu et al. U.S. Pat. No. 4,514,532 and Newman et al. U.S. Pat. No. 4,828,643, the disclosures of which are hereby incorporated herein by reference. The principal processes for the manufacture of fiberboard include: (a) wet felted/wet pressed or “wet” processes; (b) dry felted/dry pressed or “dry” processes; and, (c) wet felted/dry pressed or “wet-dry” processes. Synthetic binder resins, such as amino resins, urea-formaldehyde resins, phenol-formaldehyde resins, or modified phenol-formaldehyde resins, are often used as binders in these processes. Other binders include, but are not limited to, starches, asphalt, and gums.
Cellulosic fibers such as, for example, wood fibers are prepared by the fiberization of woody chip material in a pressurized refiner, an atmospheric refiner, a mechanical refiner, and/or a thermochemical refiner. Generally, in a wet process, the cellulosic fibers are blended in a vessel with large amounts of water to form a slurry. The slurry preferably has sufficient water content to suspend a majority of the wood fibers and preferably has a water content of at least 95 percent by weight (wt. %). The water is used to distribute a synthetic resin binder, such as a phenol-formaldehyde resin over the wood fibers. This mixture is deposited onto a water-pervious support member, such as a fine screen or a Fourdrinier wire, and pre-compressed, whereby much of the water is removed to leave a wet mat of cellulosic material having, for example, a moisture content of at least about 50 wt. % based on the weight of dry cellulosic material. The wet mat is transferred to a press and consolidated under heat and pressure to form the molded wood composite.
A wet-dry forming process can also be used to produce wood composites. Preferably, a wet-dry process begins by blending cellulosic material (e.g., wood fibers) in a vessel with a large amount of water. This slurry is then blended with a resin binder. The blend is then deposited onto a water-pervious support member, where a large percentage (e.g., 50 wt. % or more) of the water is removed, thereby leaving a wet mat of cellulosic material having a water content of about 40 wt. % to about 60 wt. %, for example. This wet mat is then transferred to a zone where much of the remaining water is removed by evaporation by heat to form a dried mat. The dried mat preferably has a moisture content of about 10 wt. % or less. The dried mat can be finished at this point or transferred to a press and consolidated under heat and pressure to form a higher density wood composite which may be a flat board or a molded product, for example. The product can be molded into various shapes or geometries depending on the intended use.
In a dry forming process, filler material, such as cellulosic fibers, is generally conveyed in a gaseous stream or by mechanical means. For example, the fibers supplied from a fiberizing apparatus (e.g., a pressurized refiner) may be coated with a thermosetting synthetic resin, such as a phenol-formaldehyde resin, in a blowline blending procedure, wherein the resin is blended with the fiber with the aid of air turbulence. Thereafter, the resin-coated fibers from the blowline can be randomly formed into a mat by air blowing the fibers onto a support member. Optionally, the fibers, either before or after formation of the mat, can be subjected to pre-press drying, for example in a tube-like dryer. The formed mat, typically having a moisture content of less than about 10 wt. %, and preferably about 5 wt. % to about 10 wt. %, then is pressed under heat and pressure to cure the thermosetting resin and to compress the mat into an integral consolidated structure.
As an alternative to conventional pressing, steam injection pressing is a consolidation step that can be used, for example, under certain circumstances in the dry and wet-dry process production of consolidated cellulosic composites. In steam injection pressing, steam is injected through perforated heating press platens, into, through, and then out of a mat that includes the synthetic resin and the filler material. The steam condenses on surfaces of the filler and heats the mat. The heat transferred by the steam to the mat as well as the heat transferred from the press platens to the mat cause the resin to cure.
The cost of manufacturing fiberboards is sensitive to the cost of raw materials. Traditionally, wood clearly has been the most important raw material in fiberboard manufacture, and because of its abundance, its costs have remained reasonably low. However, as the supply of preferred wood begins to diminish, its cost correspondingly increases. The raw material cost of wood may achieve a level where wood-alternatives may be considered viable options in the manufacture of fiberboards. Known non-wood raw material substitutes for fiberboard manufacture are limited to mineral fibers and to biological lignocellulosic fibers derived from annual plants such as bagasse, bamboo stalks, barley stalks, corn stalks, cotton stalks, flax shives, jute stalks, kenaf stalks, oat stalks, rice stalks/husks, rye stalks, sugarcane, and wheat stalks/straw. These raw materials can serve as viable substitutes for wood in wood-based fiberboards, however, these raw materials also suffer certain disadvantages in that they may not exhibit structural characteristics comparable to those of wood-based fiberboards.
Accordingly, it would be desirable to provide a nonwood-based, fibrous composite having strength and durability characteristics, and other related structural characteristics at least roughly equivalent to those of traditional wood-based, fibrous composite products. Furthermore, it would be desirable to provide nonwood-based, fibrous composites having structural characteristics superior to those of traditional wood-based, fibrous composites. It also would be desirable to provide an abundant raw material alternative to wood as a source for the fibers in the manufacture of fibrous composites.